Concerning the legacies:

I don't have legacies that reduce power cost on my LIs except for smouldering wrath power cost and on my heal equip. I just chose to neglect those and rely on the fact that there's always a LM in the raid group and there are always several types of power restoring pots available. Works fine for me.

I also tend to have legacies which are not part of my general rota - like Do not fall this Day CD - on switch LIs. That saves me a slot on my main LI which I can use to push my damage or healing output even further. Swapping LIs is so quick that it really is not a problem to do so before and after hitting Do not fall this Day. You'll be back on your main satchel before the animation of the skill is even through.